The present invention relates, in general, to hand brake assemblies for use on railway type vehicles and, more particularly, this invention relates to an apparatus to automatically activate and apply the brakes on such railway vehicle without requiring an operator to manually wind the chain on such hand brake.
Prior to the conception and development of the present invention, railway car hand brake mechanisms were well known in the art. They usually include a large, rotatable hand wheel disposed in a vertical plane and mounted on a shaft which, through a gear train, can rotate a chain drum to wind up a chain that is secured at its end remote from the chain drum to the brake rigging of the railway car. As the hand wheel is rotated in one direction, the brakes are applied and rotation of the hand wheel shaft in the opposite direction is prevented by a pawl which engages a detent wheel on the hand wheel shaft.
The brakes may be released by disengaging the pawl from the detent wheel but this causes rapid rotation of the hand wheel and the gears of the gear train. To avoid rapid rotation of the hand wheel, hand brake mechanisms have been devised which are known as xe2x80x9cquick releasexe2x80x9d mechanisms. Generally these quick release mechanisms include a releasable connecting means between the hand wheel shaft and the gear train. When the connecting means is released, the gears of the gear train rotate rapidly, without constraint by the pawl and detent wheel, but the hand wheel remains stationary.
The Association of American Railroads (AAR) promulgates specifications for the design and operation of railway car hand brake mechanisms. Vertical wheel, gear train, hand brake mechanisms are classified in three categories, namely:
(1) Standard powerxe2x80x94provides an average force on the chain of 3350 lbs. with a 125 lb. turning force applied to the rim of a wheel twenty-two inches in diameter.
(2) Intermediate powerxe2x80x94provides an average force on the chain of 4475 lbs. with a 125 lb. turning force applied to the rim of a wheel twenty-two inches in diameter.
(3) High powerxe2x80x94provides an average force on the chain of 6800 lbs. with a 125 lb. turning force applied to the rim of a wheel twenty-two inches in diameter.
After setting of the brakes, when the hand brake mechanism is released the gears of the gear train rotate rapidly. This results in the gears and other components being subjected to high forces and to shock, particularly, when the chain becomes fully let-out from the chain drum.
In recent times, the AAR has added a life cycle test to its specifications, and hand brake mechanisms which do not meet the life cycle test cannot be sold for use on railway cars operated in interchange service on United States railroads. The AAR life cycle test for quick release brakes requires that such latter brakes withstand 3000 quick release operations.
To meet such life cycle test requirements, even standard power hand brake mechanisms had to be modified when the life cycle test was adopted. When intermediate power hand brake mechanisms of the type sold prior to the adoption of the life cycle test were subjected to the life cycle test, it was found that the components thereof wore prematurely or were damaged, and it was found to be necessary to add a shock retarder, or absorber, external to the hand brake mechanism, to overcome such wear and damage. Of course, such an external shock retarder is undesirable not only because it is external to the hand brake mechanism but also because of the additional cost and because it requires field modification of the equipment on a railway car if the intermediate power hand brake mechanism is used to replace a standard power hand brake mechanism.
High power hand brake mechanisms sold prior to the adoption of, the life cycle test were similarly unable to pass the life cycle test. It should be borne in mind that such high power brake mechanisms normally have additional gears to provide the desired force on the chain, and this results in a higher speed of rotation of at least some of the gears during release of the hand brake mechanism.
Although the use of an external shock retarder might have solved the problems with the higher power hand brake mechanism, a change in the AAR specifications would have been required to permit the use of such an external shock retarder. Attempts were made to redesign the high power hand brake mechanism, such as by making it stronger, so that it would meet the life cycle test without the use of an external shock retarder, but the attempts were not successful.
One of the characteristics of railway car brakes with which the invention is concerned is that the force applied to the chain, and hence, the parts of the hand brake, is non-linear and depends on the extent to which the brakes are applied or released. Thus, as the brakes are applied, relatively little force is required to take up the slack in the chain and the brake rigging, but to meet AAR requirements, the final force on the chain must be as set forth herein before, namely, 3350 lbs. for a standard power brake, 4475 lbs. for an intermediate power brake and 6800 lbs. for a high power brake.
After slack in the rigging is taken up, which may require, for example, 5-15 inches of chain travel, the force on the chain increases exponentially, e.g. from 200 lbs. to the final value, as the brake hand wheel is further turned to set the brakes. In reaching the final value after the slack is taken up, the chain may travel only two or three inches. Similarly, when the hand brake is released, the chain force decreases exponentially and reaches a relatively small value shortly after the hand brake is released.
The present invention, according to a first aspect, provides an apparatus engageable with a hand brake assembly for automatically applying at least one brake means secured to a railway vehicle with such hand brake assembly. This apparatus includes an operating means having at least a portion thereof engageable with at least one gear of a gear assembly disposed in a housing member of such hand brake assembly. Such operating means operates such gear assembly in a direction which will cause an application of the at least one brake means. There is a source of fluid pressure connected to the operating means which periodically supplies a predetermined pressure to the operating means which is at least sufficient to cause the application of such at least one brake means. Further a means is connected to the source of fluid pressure for initiating the supply of predetermined pressure to the operating means thereby causing an automatic application of such at least one brake means by the hand brake assembly.
According to a second aspect, the present invention provides, in addition to the apparatus described above, a control means connected intermediate the operating means and the source of fluid pressure for controlling such predetermined pressure being periodically supplied to the operating means. Additionally, a venting means is connected to the operating means for venting the fluid pressure from such operating means.
In a third aspect, the present invention provides, in addition to the apparatus described above respect to the second aspect, a means connected intermediate the operating means and the control means for discontinuing the supply of the predetermined fluid pressure to the operating means thereby causing discontinuation of application of the at least one brake means.
It is, therefore, one of the primary objects of the present invention to provide an automatic application hand brake which provides a more reliable operation.
Another object of the present invention is to provide an automatic application hand brake which has incorporated therein an emergency shut-off means to stop automatic application of the hand brake.
Still another object of the present invention, is to provide an automatic application hand brake which can be retrofitted onto existing railway cars.
Yet another object of the present invention is to provide an automatic application hand brake which is relatively inexpensive to produce.
A further object to the present invention is to provide an automatic application hand brake which will exhibit a minimum of maintenance requirements.
An additional object of the present invention is to provide an automatic application hand brake which will meet the a AAR requirements for substantially all applications.
In addition to the various objects and advantages of the present invention which been described in some detail above it should be recognized that various other objects and advantages of the invention will become more readily apparent to those persons who are skilled in the relevant art from the following more detailed description of the invention, particularly, when such description is taken in conjunction with the attached drawing figures and with the appended claims.